Method, system and computer program product for verifying address generation, interlocks and bypasses

ABSTRACT

Method, system and computer program product for verifying the address generation, address generation interlocks, and address generation bypassing controls in a CPU. An exemplary embodiment includes a verification method in a processor, the method including propagating a first set general purpose register values from a first instruction to a second instruction, wherein the simulation monitor is coupled to a first stage of the instruction pipeline, and wherein the first set of general purpose register values are stored in a simulation instruction object, selecting a second set of general purpose register values, updating the first set of general purpose register values with the second set of general purpose register values and placing the second set of general purpose register values on a bus.

BACKGROUND OF THE INVENTION

This invention relates generally to hardware verification, and moreparticularly to a method, system and computer program product forverifying the address generation, address generation interlocks, andaddress generation bypassing controls in a CPU.

Address generation (AGEN), address generation interlocks (AGI) andaddress generation bypassing (AGEN Bypass) are complex functionssometimes implemented in the Instruction Dispatch Unit (IDU) of a CPU.Typically, verification of these functions is performed in unitsimulation. For example, verification in unit simulation includes: 1)driving random data on the bypass buses from sending units (e.g. FixedPoint Unit (FXU)); 2) Predicting when AGI & AGEN Bypass are going tohappen in the IDU; 3) capturing the bypass data, and storing that into asingle (software) copy of the general purpose registers (GPRs); and 4)using the GPR copy to compute a predicted AGEN, to compare against thehardware AGEN result.

However, this approach has drawbacks including requiring effectivelyduplicating logic in the IDU (the design under test) in simulation code,to predict. AGI and AGEN Bypass, which is not desirable (logic errorscan be duplicated & thus masked in the simulation code). In addition,the AGI and AGEN Bypass logic is complicated, and thus requires a lot ofcode and effort to implement and debug in simulation, including a lot ofdesigner time in explaining the design and looking at false fails, andother time consuming operations.

BRIEF SUMMARY OF THE INVENTION

An exemplary embodiment includes a verification method in a processor,the method including propagating a first set general purpose registervalues from a first instruction to a second instruction, wherein thesimulation monitor is coupled to a first stage of the instructionpipeline, and wherein the first set of general purpose register valuesare stored in a simulation instruction object, selecting a second set ofgeneral purpose register values, updating the first set of generalpurpose register values with the second set of general purpose registervalues and placing the second set of general purpose register values ona bus.

Another exemplary embodiment includes a verification method, includingperforming in a simulated instruction object: copying general purposeregister values from a preceding instruction in a general purposeregister set, performing AGEN operations on addresses in the pipelinethat access the copy of the general purpose register values and writingto a subset of general purpose registers.

A further exemplary embodiment includes a processor, including aninstruction pipeline, a simulation driver coupled to the instructionpipeline, a simulation monitor coupled to the instruction pipeline and aplurality of simulation instruction objects residing in the instructionpipeline, each of the plurality of simulation instruction objectsincluding a set of general purpose registers, an expected AGEN resultfor addresses accessing the general, purpose registers and a pipelinestage of the instruction pipeline.

BRIEF DESCRIPTION OF THE DRAWINGS

Referring now to the drawings wherein like elements are numbered alikein the several FIGURES:

FIG. 1 illustrates an exemplary embodiment of a system for verifying theaddress generation, address generation, interlocks, and addressgeneration bypassing controls in a CPU;

FIG. 2 illustrates one example of a simulation environment for a designunder test which includes AGEN, AGI and AGEN Bypass logic;

FIG. 3 illustrates one example of the pipeline stages of a CPU designwhich include AGEN, AGI and AGEN Bypass logic;

FIG. 4 illustrates one example of Simulation objects which include a setof GPRs for each instruction, along with expected AGEN results and thecurrent pipe stage for each instruction;

FIG. 5 illustrates a method for verifying the address generation,address generation interlocks, and address generation bypassing controlsin a CPU in accordance with exemplary embodiments; and

FIG. 6 illustrates one example of an actual instruction stream insimulation, along with the way the AGEN results are calculated for theexpected results.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

In an exemplary embodiment, the systems and methods described hereinretain a set of (software) GPRs with each instruction in a pipeline, andpropagate GPR values from older to younger instructions. In an exemplaryembodiment, AGEN results are computed for future instructions, withoutregard to whether an AGI or AGEN Bypass is needed.

FIG. 1 illustrates an exemplary embodiment of a system 100 for verifyingthe address generation, address generation interlocks, and addressgeneration bypassing controls in a CPU. The methods described herein canbe implemented in software (e.g., firmware), hardware, or a combinationthereof. In exemplary embodiments, the methods described herein areimplemented in software, as an executable program, and is executed by aspecial, or general-purpose digital computer, such as a personalcomputer, workstation, minicomputer, or mainframe computer. The system100 therefore includes general-purpose computer 101.

In exemplary embodiments, in terms of hardware architecture, as shown inFIG. 1, the computer 101 includes a processor 105, memory 110 coupled toa memory controller 115, and one or more input and/or output (I/O)devices 140, 145 (or peripherals) that are communicatively coupled via alocal input/output controller 135. The input/output controller 135 canbe, for example but not limited to, one or more buses or other wired orwireless connections, as is known in the art. The input/outputcontroller 135 may have additional elements, which are omitted forsimplicity, such as controllers, buffers (caches), drivers, repeaters,and receivers, to enable communications. Further, the local interfacemay include address, control, and/or data connections to enableappropriate communications among the aforementioned components.

The processor 105 is a hardware device for executing software,particularly that stored in memory 110. The processor 105 can be anycustom, made or commercially available processor, a central processingunit (CPU), an auxiliary processor among several processors associatedwith the computer 101, a semiconductor based microprocessor (in the formof a microchip or chip set), a macroprocessor, or generally any devicefor executing software instructions.

The memory 110 can include any one or combination of volatile memoryelements (e.g., random access memory (RAM, such as DRAM, SRAM, SDRAM,etc.)) and nonvolatile memory elements (e.g., ROM, erasable programmableread only memory (EPROM), electronically erasable programmable read onlymemory (EEPROM), programmable read only memory (PROM), tape, compactdisc read only memory (CD-ROM), disk, diskette, cartridge, cassette orthe like, etc.). Moreover, the memory 110 may incorporate electronic,magnetic, optical, and/or other types of storage media. Note that thememory 110 can have a distributed architecture, where various componentsare situated remote from one another, but can be accessed by theprocessor 105.

The software in memory 110 may include one or more separate programs,each of which comprises an ordered listing of executable instructionsfor implementing logical functions. In the example of FIG. 1, thesoftware in the memory 110 includes the verification methods describedherein in accordance with exemplary embodiments and a suitable operatingsystem (OS) 111. The operating system 111 essentially controls theexecution of other computer programs, such the verification systems andmethods described herein, and provides scheduling, input-output control,file and data management, memory management, and communication controland related services.

The verification methods described herein may be in the form of a sourceprogram, executable program (object code), script, or any other entitycomprising a set of instructions to be performed. When a source program,then the program needs to be translated via a compiler, assembler,interpreter, or the like, which may or may not be included within thememory 110, so as to operate properly in connection with the OS 111.Furthermore, the verification methods can he written as an objectoriented programming language, which has classes of data and methods, ora procedure programming language, which has routines, subroutines,and/or functions.

In exemplary embodiments, a conventional keyboard 150 and mouse 155 canbe coupled to the input/output controller 135. Other output devices suchas the I/O devices 140, 145 may include input devices, for example butnot limited to a printer, a scanner, microphone, and the like. Finally,the I/O devices 140, 145 may further include devices that communicateboth inputs and outputs, for instance but not limited to, a networkinterlace card (NIC) or modulator/demodulator (for accessing otherfiles, devices, systems, or a network), a radio frequency (RF) or othertransceiver, a telephonic interface, a bridge, a router, and the like.The system 100 can further include a display controller 125 coupled to adisplay 130. In exemplary embodiments, the system 100 can furtherinclude a network interface 160 for coupling to a network 165. Thenetwork 165 can be an IP-based network for communication between thecomputer 101 and any external server, client and the like via abroadband connection. The network 165 transmits and receives databetween the computer 101 and external systems. In exemplary embodiments,network 165 can be a managed IP network administered by a serviceprovider. The network 165 may be implemented in a wireless fashion,e.g., using wireless protocols and technologies, such as WiFi, WiMax,etc. The network 165 can also be a packet-switched network such as alocal area network, wide area network, metropolitan area network,internet network, or other similar type of network environment. Thenetwork 165 may be a fixed wireless network, a wireless local areanetwork (LAN), a wireless wide area network (WAN) a personal areanetwork (PAN), a virtual private network (VPN), intranet or othersuitable network system and includes equipment for receiving andtransmitting signals.

If the computer 101 is a PC, workstation, intelligent device or thelike, the software in the memory 110 may further include a basic inputoutput system (BIOS) (omitted for simplicity). The BIOS is a set ofessential software routines that initialize and test hardware atstartup, start the OS 111, and support the transfer of data among thehardware devices. The BIOS is stored in ROM so that the BIOS can beexecuted when the computer 101 is activated.

When the computer 101 is in operation, the processor 105 is configuredto execute software stored within the memory 110, to communicate data toand from the memory 110, and to generally control operations of thecomputer 101 pursuant to the software. The verification methodsdescribed herein and the OS 111, in whole or in part, but typically thelatter, are read by the processor 105, perhaps buffered within theprocessor 105, and then executed.

When the systems and methods described herein are implemented insoftware, as is shown in FIG. 1, it the methods can be stored on anycomputer readable medium, such as storage 120, for use by or inconnection with any computer related system or method. In the context ofthis document, a computer readable medium is an electronic, magnetic,optical, or other physical device or means that can contain or store acomputer program for use by or in connection with a computer relatedsystem or method. The verification, methods described herein can beembodied in any computer-readable medium for use by or in connectionwith an instruction execution system, apparatus, or device, such as acomputer-based system, processor-containing system, or other system thatcan fetch the instructions from the instruction execution system,apparatus, or device and execute the instructions. In exemplaryembodiments, a “computer-readable medium” can be any means that canstore, communicate, propagate, or transport the program for use by or inconnection with the instruction execution system, apparatus, or device.The computer readable medium can be, for example but not limited to, anelectronic, magnetic, optical, electromagnetic, infrared, orsemiconductor system, apparatus, device, or propagation medium. Morespecific examples (a non-exhaustive list) of the computer-readablemedium would include the following: an electrical connection(electronic) having one or more wires, a portable computer diskette(magnetic), a random access memory (RAM) (electronic), a read-onlymemory (ROM) (electronic), an erasable programmable read-only memory(EPROM, EEPROM, or Flash memory) (electronic), an optical fiber(optical), and a portable compact disc read-only memory (CDROM)(optical). Note that the computer-readable medium could even be paper oranother suitable medium upon which the program is printed, as theprogram can be electronically captured, via for instance opticalscanning of the paper or other medium, then compiled, interpreted orotherwise processed in a suitable manner If necessary, and then storedin a computer memory.

In exemplary embodiments, where the verification methods are implementedin hardware, the verification methods described herein can implementedwith any or a combination of the following technologies, which are eachwell known in the art: a discrete logic circuit(s) having logic gatesfor implementing logic functions upon data signals, an applicationspecific integrated circuit (ASIC) having appropriate combinationallogic gates, a programmable gate array(s) (PGA), a field programmablegate array (FPGA), etc.

FIG. 2 illustrates a block diagram of a simulation environment 200 thatcan include a simulation driver 201 coupled to a design under test 202(e.g., the processor 105) coupled to a simulation monitor 203. In anexemplary embodiment, the simulation driver 201 is responsible fordriving instructions into the IDU (Design under Test) 202, as well asdriving execution results (new GPR values) from other execution unitsinto IDU, The IDU includes the AGEN, AGI and AGEN Bypass logic that areto be verified, in an exemplary embodiment, the simulation monitor 203checks the AGEN results on all possible cycles.

FIG. 3 illustrates a block diagram of a set of pipeline stages 300 for aCPU (e.g., the processor 105) in accordance with an exemplaryembodiment. In an exemplary embodiment, the pipeline 300 can includestages including, but not limited to: Ifetch 305; Dee 310; Disp 315;Agen0 320; Agen1 325; Dfetch 330; Exec 335; Write 340; PA1 345; and PA2350. In an exemplary embodiment, a simulation monitor 301 coupled to thepipeline 300, checks an AGEN result in the pipeline stages 300, the AGENresult denoted ‘Agen1’. In an exemplary embodiment, if an instructionupdates a GPR, a simulation driver 302 coupled to the pipeline stages300 drives new GPR values on the AGEN Bypass (if allowed for theinstruction) and execution result, buses in the appropriate cycles(pipeline stages).

FIG. 4 depicts a simulation instruction object diagram 400 representingan instruction in accordance with an exemplary embodiment. Eachsimulation instruction object contains a set of GPR values 401, anexpected AGEN result 402, and a pipeline stage 403. In an exemplaryembodiment, the GPR values are propagated from instruction (i−1)(oldest) to instruction (i) to instruction (i+1) (newest). In anexemplary embodiment, the expected AGEN result is computed once the GPRvalues are propagated in the Disp 315 pipeline stage (see FIG. 3), whichis prior to the hardware design beginning the AGEN. In addition tochecking the expected AGEN result, the simulation monitor 203, 301 isalso responsible for propagating the GPR values from one instruction tothe next, and keeping track of the pipeline stage for each instruction.In an exemplary embodiment, the simulation driver 201, 302 assigns newrandom values for GPRs for instructions that update GPRs, after the GPRvalues have been propagated from the prior instruction. The new randomvalues are saved in the simulation instruction object, and are used bythe simulation driver 201, 302 to drive the AGEN Bypass and executionresult buses in the appropriate pipeline stages.

FIG. 5 illustrates a method 500 for verifying the address generation,address generation interlocks, and address generation bypassing controlsin a CPU in accordance with exemplary embodiments. As described above,in an exemplary embodiment each instruction in the instruction pipelineincludes a simulated instruction object having a full set of GPRs (orMilli-GPRs), an expected AGEN result, and a pipeline stage. As eachinstruction in the pipeline is dispatched through the pipeline, at block510, the simulated instruction object copies all the GPR values from thepreceding instruction into the instruction's GPR set. At block 520 thesimulated instruction object performs AGEN for any addresses in thepipeline that are using the instruction's GPR copy, and then saves theexpected AGEN result for a later comparison. At block 530, for any GPRsthat the instruction writes, the simulated instruction object assignsnew random GPR values in its own GPR set. The simulation driver 201, 302then drives the bypass buses from any sending units with the new GPRvalues, at block 540. The simulation monitor 203, 301 compares theactual AGEN result with the expected AGEN results at block 550. Asdiscussed above, the method 500 ensures that the AGEN results can alwaysbe predicted for an instruction based on GPR values from priorinstructions, without knowing whether or not an AGI or AGI bypass isgoing to occur.

Therefore, it is appreciated that as each instruction, J, at a dispatchtime, full knowledge of all GPR values are known from the precedinginstruction J-1. Therefore, checking for the correct AGEN result for Jis determined from the GPR values associated with the instruction objectassociated with the preceding instruction J-1 (i.e., to compute theexpected AGEN result).

FIG. 6 illustrates a sample instruction stream 600 in accordance withexemplary embodiments. As illustrated, the instruction stream 600illustrates the propagation of GPRs from one instruction to the nextinstruction. In addition, the instruction stream illustrates assignmentof new random GPR values. The instruction stream 600 further illustratescomputation of the expected AGEN result. In particular, in 601, the GPRvalues for the L instruction are propagated from the precedinginstruction. The expected AGEN result is then computed using thosepropagated values in 602. Finally, since the L instruction updates aGPR, a new random value for the GPR is chosen in 603. All of theseactions are performed in the Disp 315 pipeline stage for the Linstruction—that is prior to the first AGEN cycle. In an exemplaryembodiment, as the L instruction progresses through the pipeline 300,the simulation driver 201, 302 puts the new value of GPR2 on the bypassbuses and final execution result bus in the appropriate pipeline 300stages. The IDU may or may not choose to accept the bypass data. In anexemplary embodiment, from a verification perspective the IDU choosingor not choosing the bypass data is not critical. For any instruction,the expected AGEN result is the correct AGEN result, without regard towhether or not there is an AGI or AGEN Bypass. The AGEN result can bechecked in any cycle that it's needed (e.g. Agen1 325).

In an exemplary embodiment, the systems and methods described herein canalso be applied to the Millicode mode; the Instruction Simulation Objectis extended to include Milli-GPRs, and those values are propagated frominstruction to instruction. The Milli-GPRs are then used to compute theexpected AGEN result.

Technical effects and benefits include verification of AGEN, AGI, andAGEN Bypass hardware by treating the design under test as a ‘black box’,and not having to duplicate any of the hardware logic in our simulationcode to predict AGI and AGEN Bypass.

As described above, the embodiments of the invention may be embodied inthe form of computer-implemented processes and apparatuses forpracticing those processes. Embodiments of the invention may also beembodied in the form of computer program code containing instructionsembodied in tangible media, such as floppy diskettes, CD-ROMs, harddrives, or any other computer-readable storage medium, wherein, when thecomputer program code is loaded into and executed by a computer, thecomputer becomes an apparatus for practicing the invention. The presentinvention can also he embodied in the form of computer program code, forexample, whether stored in a storage medium, loaded into and/or executedby a computer, or transmitted over some transmission medium, such asover electrical wiring or cabling, through fiber optics, or viaelectromagnetic radiation, wherein, when the computer program code isloaded into and executed by a computer, the computer becomes anapparatus for practicing the invention. When implemented on ageneral-purpose microprocessor, the computer program code segmentsconfigure the microprocessor to create specific logic circuits.

While the invention has been described with reference to exemplaryembodiments, it will be understood by those skilled in the art thatvarious changes may be made and equivalents may be substituted forelements thereof without departing from the scope of the invention. Inaddition, many modifications may be made to adapt a particular situationor material to the teachings of the invention without, departing fromthe essential scope thereof. Therefore, it is intended that theinvention not be limited to the particular embodiment disclosed as thebest mode contemplated for carrying out this invention, but that theinvention will include all embodiments falling within the scope of theappended claims. Moreover, the use of the terms first, second, etc. donot denote any order or importance, but rather the terms first, second,etc. are used to distinguish one element from another.

1. In a processor simulator for simulating a processor having aninstruction pipeline and an address generation (AGEN) bypass-bus, averification method, comprising: propagating a first set of generalpurpose register values from a first instruction to a secondinstruction, wherein a simulation monitor is coupled to a simulatedfirst stage of the instruction pipeline, and wherein the first set ofgeneral purpose register values are stored in a simulation instructionobject, wherein the AGEN bypass-bus is simulated in the simulationmonitor and wherein AGEN results are sent by way of the simulated AGENbypass bus to the instruction pipeline; in response to a computation ofan expected AGEN result in the simulated instruction object, selecting asecond set of general purpose register values; updating the first set ofgeneral purpose register values with the second set of general purposeregister values; and placing the second set of general purpose registervalues on a simulated bus, wherein at a dispatch time of the secondinstruction in the pipeline, general purpose register values for thefirst instruction are known, wherein an AGEN result for the secondinstruction is determined from the general purpose register valuesassociated with an instruction object associated with the firstinstruction, the determining independent of whether at least one ofaddress generation interlock (AGI) and AGI bypass occurs.
 2. The methodas claimed in claim 1 wherein a simulation driver places the second setof general purpose register values on the simulated AGEN bypass-bus. 3.The method as claimed in claim 1 wherein the simulation driver places asecond set of general purpose register values on an execution result buscoupled to the processor.
 4. The method as claimed in claim 1 whereinthe simulation instruction object includes a pipeline stage associatedwith the expected AGEN value and the first set of general purposeregister values.
 5. The method as claimed in claim 4 wherein thesimulation driver places the second set of general purpose registervalues on the simulated bus in response to the second instructionpropagated in the pipeline stage associated with the expected AGENvalue.
 6. The method as claimed in claim 1 wherein the first set generalpurpose register values are propagated from the first instruction to thesecond instruction prior to a microprocessor AGEN cycle.
 7. The methodas claimed in claim 6 further comprising the simulation monitorcomparing the expected AGEN result with an actual hardware AGEN resultgenerated by the microprocessor AGEN cycle.
 8. The method as claimed inclaim 6 wherein the first set general purpose register values arepropagated from the first instruction to the second instruction in aDispatch stage of the instruction pipeline.
 9. A verification method fora processor model, comprising: for each instruction in a processorpipeline, performing in a simulated instruction object: copying generalpurpose register values from a preceding instruction in a generalpurpose register set; performing address generation (AGEN) operationsfrom a simulation monitor that includes a simulated AGEN bypass-bus onaddresses in the pipeline that access the copy of the general purposeregister values; writing to a subset of general purpose registers,wherein at a dispatch time of a second instruction in the pipeline,general purpose register values for a first instruction are known,wherein an AGEN result for the second instruction is determined from thegeneral purpose register values associated with an instruction objectassociated with the first instruction, the determining independent ofwhether at least one of address generation interlock (AGI) and AGIbypass occurs.
 10. The method as claimed in claim 9 further comprising:for each of the subset of general purpose registers: assigning newrandom general purpose register values to the general purpose registerset.
 11. The method as claimed in claim 10 further comprising driving abypass bus from a sending unit with the new random general purposeregister values.
 12. The method as claimed in claim 11 wherein asimulation driver coupled to the simulated instruction object drives thebypass bus from the sending unit with the new random general purposeregister values.
 13. The method as claimed in claim 9 further comprisingsaving an expected AGEN result.
 14. The method as claimed in claim 13further comprising comparing an actual AGEN result with the expectedAGEN result.
 15. The method as claimed in claim 14 wherein a simulationmonitor coupled to the simulated instruction object compares the actualAGEN result with the expected AGEN result.
 16. A method for simulating aprocessor, comprising: simulating an instruction pipeline; simulating asimulation driver coupled to the instruction pipeline; simulating asimulation monitor coupled to the instruction pipeline; and simulating aplurality of simulation instruction objects residing in the instructionpipeline, each of the plurality of simulation instruction objectsincluding: a set of general purpose registers; an expected addressgeneration (AGEN) result from a simulated AGEN bypass-bus residing inthe simulation monitor for addresses accessing the general purposeregisters; and a pipeline stage of the instruction pipeline wherein at adispatch time of a second instruction in the pipeline, general purposeregister values for a first instruction are known, wherein an AGENresult for the second instruction is determined from the general purposeregister values associated with an instruction object associated withthe first instruction, the determining independent of whether at leastone of address generation interlock (AGI) and AGI bypass occurs.
 17. Themethod as claimed in claim 16 wherein the simulation monitor isconfigured to propagate a first set of general purpose register valuesfrom a first instruction to a second instruction in the instructionpipeline, prior to a processor AGEN cycle.
 18. The method as claimed inclaim 17 wherein the simulation driver is configured to select a secondset of general purpose register values for instructions in theinstruction pipeline that update the set of general purpose registersafter the expected AGEN result is computed.
 19. The method as claimed inclaim 18 wherein the simulation driver is configured to a second set ofgeneral purpose register values on a processor bus.
 20. The method asclaimed in claim 19 wherein the simulation monitor is further configuredto compare the expected AGEN result with an actual AGEN result in anassociated stage of the instruction pipeline.
 21. A computer programproduct for simulating a processor having an instruction pipeline and anaddress generation (AGEN) bypass bus, the computer program productincluding a non-transitory computer readable medium storing instructionsfor causing a computer to implement a verification method, theverification method comprising: propagating a first set of generalpurpose register values from a first instruction to a secondinstruction, wherein a simulation monitor is coupled to a simulatedfirst stage of the instruction pipeline, and wherein the first set ofgeneral purpose register values are stored in a simulation instructionobject, wherein the AGEN bypass bus is simulated in the simulationmonitor and wherein AGEN results are sent by way of the simulated AGENbypass bus to the instruction pipeline; in response to a computation ofan expected AGEN result in the simulated instruction object, selecting asecond set of general purpose register values; updating the first set ofgeneral purpose register values with the second set of general purposeregister values; and placing the second set of general purpose registervalues on a simulated bus, wherein at a dispatch time of the secondinstruction in the pipeline, general purpose register values for thefirst instruction are known, wherein an AGEN result for the secondinstruction is determined from the general purpose register valuesassociated with an instruction object associated with the firstinstruction, the determining independent of whether at least one ofaddress generation interlock (AGI) and AGI bypass occurs.
 22. A computerprogram product for simulating a processor, the computer program productincluding a non-transitory computer readable medium storing instructionsfor causing a computer to implement a method, the method comprising:simulating an instruction pipeline; simulating a simulation drivercoupled to the instruction pipeline; simulating a simulation monitorcoupled to the instruction pipeline; and simulating a plurality ofsimulation instruction objects residing in the instruction pipeline,each of the plurality of simulation instruction objects including: a setof general purpose registers; an expected address generation (AGEN)result from a simulated AGEN bypass-bus residing in the simulationmonitor for addresses accessing the general purpose registers; and apipeline stage of the instruction pipeline, wherein at a dispatch timeof a second instruction in the pipeline, general purpose register valuesfor a first instruction are known, an AGEN result for the secondinstruction is determined from the general purpose register valuesassociated with an instruction object associated with the firstinstruction, the determining independent of whether at least one ofaddress generation interlock (AGI) and AGI bypass occurs.
 23. Thecomputer program product as claimed in claim 22 wherein the simulationmonitor is configured to propagate a first set of general purposeregister values from a first instruction to a second instruction in theinstruction pipeline, prior to a processor AGEN cycle.
 24. The computerprogram product as claimed in claim 23 wherein the simulation driver isconfigured to select a second set of general purpose register values forinstructions in the instruction pipeline that update the set of generalpurpose registers after the expected AGEN result is computed.
 25. Thecomputer program product as claimed in claim 24 wherein the simulationdriver is configured to second set of general purpose register values ona processor bus.